/*-------------------------------------------------------------------------
 *
 * tuptoaster.c
 *      Support routines for external and compressed storage of
 *      variable size attributes.
 *
 * Copyright (c) 2000-2017, PostgreSQL Global Development Group
 *
 * This source code file contains modifications made by THL A29 Limited ("Tencent Modifications").
 * All Tencent Modifications are Copyright (C) 2023 THL A29 Limited.
 *
 * IDENTIFICATION
 *      src/backend/access/heap/tuptoaster.c
 *
 *
 * INTERFACE ROUTINES
 *        toast_insert_or_update -
 *            Try to make a given tuple fit into one page by compressing
 *            or moving off attributes
 *
 *        toast_delete -
 *            Reclaim toast storage when a tuple is deleted
 *
 *        heap_tuple_untoast_attr -
 *            Fetch back a given value from the "secondary" relation
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <unistd.h>
#include <fcntl.h>

#include "access/genam.h"
#include "access/heapam.h"
#include "access/tuptoaster.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "common/pg_lzcompress.h"
#include "miscadmin.h"
#include "utils/expandeddatum.h"
#include "utils/fmgroids.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"
#include "utils/typcache.h"
#include "utils/tqual.h"


#undef TOAST_DEBUG

/*
 *    The information at the start of the compressed toast data.
 */
typedef struct toast_compress_header
{
    int32        vl_len_;        /* varlena header (do not touch directly!) */
    int32        rawsize;
} toast_compress_header;

/*
 * Utilities for manipulation of header information for compressed
 * toast entries.
 */
#define TOAST_COMPRESS_HDRSZ        ((int32) sizeof(toast_compress_header))
#define TOAST_COMPRESS_RAWSIZE(ptr) (((toast_compress_header *) (ptr))->rawsize)
#define TOAST_COMPRESS_RAWDATA(ptr) \
    (((char *) (ptr)) + TOAST_COMPRESS_HDRSZ)
#define TOAST_COMPRESS_SET_RAWSIZE(ptr, len) \
    (((toast_compress_header *) (ptr))->rawsize = (len))

static void toast_delete_datum(Relation rel, Datum value, bool is_speculative);
static Datum toast_save_datum(Relation rel, Datum value,
                 struct varlena *oldexternal, int options
#ifdef _SHARDING_
                 , ShardID sid
#endif
                );
static bool toastrel_valueid_exists(Relation toastrel, Oid valueid);
static bool toastid_valueid_exists(Oid toastrelid, Oid valueid);
static struct varlena *toast_fetch_datum(struct varlena *attr);
static struct varlena *toast_fetch_datum_slice(struct varlena *attr,
                        int32 sliceoffset, int32 length);
static struct varlena *toast_decompress_datum(struct varlena *attr);
static int toast_open_indexes(Relation toastrel,
                   LOCKMODE lock,
                   Relation **toastidxs,
                   int *num_indexes);
static void toast_close_indexes(Relation *toastidxs, int num_indexes,
                    LOCKMODE lock);
static void init_toast_snapshot(Snapshot toast_snapshot);


/* ----------
 * heap_tuple_fetch_attr -
 *
 *    Public entry point to get back a toasted value from
 *    external source (possibly still in compressed format).
 *
 * This will return a datum that contains all the data internally, ie, not
 * relying on external storage or memory, but it can still be compressed or
 * have a short header.  Note some callers assume that if the input is an
 * EXTERNAL datum, the result will be a pfree'able chunk.
 * ----------
 */
struct varlena *
heap_tuple_fetch_attr(struct varlena *attr)
{
    struct varlena *result;

    if (VARATT_IS_EXTERNAL_ONDISK(attr))
    {
        /*
         * This is an external stored plain value
         */
        result = toast_fetch_datum(attr);
    }
    else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
    {
        /*
         * This is an indirect pointer --- dereference it
         */
        struct varatt_indirect redirect;

        VARATT_EXTERNAL_GET_POINTER(redirect, attr);
        attr = (struct varlena *) redirect.pointer;

        /* nested indirect Datums aren't allowed */
        Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));

        /* recurse if value is still external in some other way */
        if (VARATT_IS_EXTERNAL(attr))
            return heap_tuple_fetch_attr(attr);

        /*
         * Copy into the caller's memory context, in case caller tries to
         * pfree the result.
         */
        result = (struct varlena *) palloc(VARSIZE_ANY(attr));
        memcpy(result, attr, VARSIZE_ANY(attr));
    }
    else if (VARATT_IS_EXTERNAL_EXPANDED(attr))
    {
        /*
         * This is an expanded-object pointer --- get flat format
         */
        ExpandedObjectHeader *eoh;
        Size        resultsize;

        eoh = DatumGetEOHP(PointerGetDatum(attr));
        resultsize = EOH_get_flat_size(eoh);
        result = (struct varlena *) palloc(resultsize);
        EOH_flatten_into(eoh, (void *) result, resultsize);
    }
    else
    {
        /*
         * This is a plain value inside of the main tuple - why am I called?
         */
        result = attr;
    }

    return result;
}


/* ----------
 * heap_tuple_untoast_attr -
 *
 *    Public entry point to get back a toasted value from compression
 *    or external storage.  The result is always non-extended varlena form.
 *
 * Note some callers assume that if the input is an EXTERNAL or COMPRESSED
 * datum, the result will be a pfree'able chunk.
 * ----------
 */
struct varlena *
heap_tuple_untoast_attr(struct varlena *attr)
{// #lizard forgives
    if (VARATT_IS_EXTERNAL_ONDISK(attr))
    {
        /*
         * This is an externally stored datum --- fetch it back from there
         */
        attr = toast_fetch_datum(attr);
        /* If it's compressed, decompress it */
        if (VARATT_IS_COMPRESSED(attr))
        {
            struct varlena *tmp = attr;

            attr = toast_decompress_datum(tmp);
            pfree(tmp);
        }
    }
    else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
    {
        /*
         * This is an indirect pointer --- dereference it
         */
        struct varatt_indirect redirect;

        VARATT_EXTERNAL_GET_POINTER(redirect, attr);
        attr = (struct varlena *) redirect.pointer;

        /* nested indirect Datums aren't allowed */
        Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));

        /* recurse in case value is still extended in some other way */
        attr = heap_tuple_untoast_attr(attr);

        /* if it isn't, we'd better copy it */
        if (attr == (struct varlena *) redirect.pointer)
        {
            struct varlena *result;

            result = (struct varlena *) palloc(VARSIZE_ANY(attr));
            memcpy(result, attr, VARSIZE_ANY(attr));
            attr = result;
        }
    }
    else if (VARATT_IS_EXTERNAL_EXPANDED(attr))
    {
        /*
         * This is an expanded-object pointer --- get flat format
         */
        attr = heap_tuple_fetch_attr(attr);
        /* flatteners are not allowed to produce compressed/short output */
        Assert(!VARATT_IS_EXTENDED(attr));
    }
    else if (VARATT_IS_COMPRESSED(attr))
    {
        /*
         * This is a compressed value inside of the main tuple
         */
        attr = toast_decompress_datum(attr);
    }
    else if (VARATT_IS_SHORT(attr))
    {
        /*
         * This is a short-header varlena --- convert to 4-byte header format
         */
        Size        data_size = VARSIZE_SHORT(attr) - VARHDRSZ_SHORT;
        Size        new_size = data_size + VARHDRSZ;
        struct varlena *new_attr;

        new_attr = (struct varlena *) palloc(new_size);
        SET_VARSIZE(new_attr, new_size);
        memcpy(VARDATA(new_attr), VARDATA_SHORT(attr), data_size);
        attr = new_attr;
    }

    return attr;
}


/* ----------
 * heap_tuple_untoast_attr_slice -
 *
 *        Public entry point to get back part of a toasted value
 *        from compression or external storage.
 * ----------
 */
struct varlena *
heap_tuple_untoast_attr_slice(struct varlena *attr,
                              int32 sliceoffset, int32 slicelength)
{// #lizard forgives
    struct varlena *preslice;
    struct varlena *result;
    char       *attrdata;
    int32        attrsize;

    if (VARATT_IS_EXTERNAL_ONDISK(attr))
    {
        struct varatt_external toast_pointer;

        VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);

        /* fast path for non-compressed external datums */
        if (!VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
            return toast_fetch_datum_slice(attr, sliceoffset, slicelength);

        /* fetch it back (compressed marker will get set automatically) */
        preslice = toast_fetch_datum(attr);
    }
    else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
    {
        struct varatt_indirect redirect;

        VARATT_EXTERNAL_GET_POINTER(redirect, attr);

        /* nested indirect Datums aren't allowed */
        Assert(!VARATT_IS_EXTERNAL_INDIRECT(redirect.pointer));

        return heap_tuple_untoast_attr_slice(redirect.pointer,
                                             sliceoffset, slicelength);
    }
    else if (VARATT_IS_EXTERNAL_EXPANDED(attr))
    {
        /* pass it off to heap_tuple_fetch_attr to flatten */
        preslice = heap_tuple_fetch_attr(attr);
    }
    else
        preslice = attr;

    Assert(!VARATT_IS_EXTERNAL(preslice));

    if (VARATT_IS_COMPRESSED(preslice))
    {
        struct varlena *tmp = preslice;

        preslice = toast_decompress_datum(tmp);

        if (tmp != attr)
            pfree(tmp);
    }

    if (VARATT_IS_SHORT(preslice))
    {
        attrdata = VARDATA_SHORT(preslice);
        attrsize = VARSIZE_SHORT(preslice) - VARHDRSZ_SHORT;
    }
    else
    {
        attrdata = VARDATA(preslice);
        attrsize = VARSIZE(preslice) - VARHDRSZ;
    }

    /* slicing of datum for compressed cases and plain value */

    if (sliceoffset >= attrsize)
    {
        sliceoffset = 0;
        slicelength = 0;
    }

    if (((sliceoffset + slicelength) > attrsize) || slicelength < 0)
        slicelength = attrsize - sliceoffset;

    result = (struct varlena *) palloc(slicelength + VARHDRSZ);
    SET_VARSIZE(result, slicelength + VARHDRSZ);

    memcpy(VARDATA(result), attrdata + sliceoffset, slicelength);

    if (preslice != attr)
        pfree(preslice);

    return result;
}


/* ----------
 * toast_raw_datum_size -
 *
 *    Return the raw (detoasted) size of a varlena datum
 *    (including the VARHDRSZ header)
 * ----------
 */
Size
toast_raw_datum_size(Datum value)
{
    struct varlena *attr = (struct varlena *) DatumGetPointer(value);
    Size        result;

    if (VARATT_IS_EXTERNAL_ONDISK(attr))
    {
        /* va_rawsize is the size of the original datum -- including header */
        struct varatt_external toast_pointer;

        VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
        result = toast_pointer.va_rawsize;
    }
    else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
    {
        struct varatt_indirect toast_pointer;

        VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);

        /* nested indirect Datums aren't allowed */
        Assert(!VARATT_IS_EXTERNAL_INDIRECT(toast_pointer.pointer));

        return toast_raw_datum_size(PointerGetDatum(toast_pointer.pointer));
    }
    else if (VARATT_IS_EXTERNAL_EXPANDED(attr))
    {
        result = EOH_get_flat_size(DatumGetEOHP(value));
    }
    else if (VARATT_IS_COMPRESSED(attr))
    {
        /* here, va_rawsize is just the payload size */
        result = VARRAWSIZE_4B_C(attr) + VARHDRSZ;
    }
    else if (VARATT_IS_SHORT(attr))
    {
        /*
         * we have to normalize the header length to VARHDRSZ or else the
         * callers of this function will be confused.
         */
        result = VARSIZE_SHORT(attr) - VARHDRSZ_SHORT + VARHDRSZ;
    }
    else
    {
        /* plain untoasted datum */
        result = VARSIZE(attr);
    }
    return result;
}

/* ----------
 * toast_datum_size
 *
 *    Return the physical storage size (possibly compressed) of a varlena datum
 * ----------
 */
Size
toast_datum_size(Datum value)
{
    struct varlena *attr = (struct varlena *) DatumGetPointer(value);
    Size        result;

    if (VARATT_IS_EXTERNAL_ONDISK(attr))
    {
        /*
         * Attribute is stored externally - return the extsize whether
         * compressed or not.  We do not count the size of the toast pointer
         * ... should we?
         */
        struct varatt_external toast_pointer;

        VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
        result = toast_pointer.va_extsize;
    }
    else if (VARATT_IS_EXTERNAL_INDIRECT(attr))
    {
        struct varatt_indirect toast_pointer;

        VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);

        /* nested indirect Datums aren't allowed */
        Assert(!VARATT_IS_EXTERNAL_INDIRECT(attr));

        return toast_datum_size(PointerGetDatum(toast_pointer.pointer));
    }
    else if (VARATT_IS_EXTERNAL_EXPANDED(attr))
    {
        result = EOH_get_flat_size(DatumGetEOHP(value));
    }
    else if (VARATT_IS_SHORT(attr))
    {
        result = VARSIZE_SHORT(attr);
    }
    else
    {
        /*
         * Attribute is stored inline either compressed or not, just calculate
         * the size of the datum in either case.
         */
        result = VARSIZE(attr);
    }
    return result;
}


/* ----------
 * toast_delete -
 *
 *    Cascaded delete toast-entries on DELETE
 * ----------
 */
void
toast_delete(Relation rel, HeapTuple oldtup, bool is_speculative)
{
    TupleDesc    tupleDesc;
    Form_pg_attribute *att;
    int            numAttrs;
    int            i;
    Datum        toast_values[MaxHeapAttributeNumber];
    bool        toast_isnull[MaxHeapAttributeNumber];

    /*
     * We should only ever be called for tuples of plain relations or
     * materialized views --- recursing on a toast rel is bad news.
     */
    Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
           rel->rd_rel->relkind == RELKIND_MATVIEW);

    /*
     * Get the tuple descriptor and break down the tuple into fields.
     *
     * NOTE: it's debatable whether to use heap_deform_tuple() here or just
     * heap_getattr() only the varlena columns.  The latter could win if there
     * are few varlena columns and many non-varlena ones. However,
     * heap_deform_tuple costs only O(N) while the heap_getattr way would cost
     * O(N^2) if there are many varlena columns, so it seems better to err on
     * the side of linear cost.  (We won't even be here unless there's at
     * least one varlena column, by the way.)
     */
    tupleDesc = rel->rd_att;
    att = tupleDesc->attrs;
    numAttrs = tupleDesc->natts;

    Assert(numAttrs <= MaxHeapAttributeNumber);
    heap_deform_tuple(oldtup, tupleDesc, toast_values, toast_isnull);

    /*
     * Check for external stored attributes and delete them from the secondary
     * relation.
     */
    for (i = 0; i < numAttrs; i++)
    {
        if (att[i]->attlen == -1)
        {
            Datum        value = toast_values[i];

            if (toast_isnull[i])
                continue;
            else if (VARATT_IS_EXTERNAL_ONDISK(PointerGetDatum(value)))
                toast_delete_datum(rel, value, is_speculative);
        }
    }
}


/* ----------
 * toast_insert_or_update -
 *
 *    Delete no-longer-used toast-entries and create new ones to
 *    make the new tuple fit on INSERT or UPDATE
 *
 * Inputs:
 *    newtup: the candidate new tuple to be inserted
 *    oldtup: the old row version for UPDATE, or NULL for INSERT
 *    options: options to be passed to heap_insert() for toast rows
 * Result:
 *    either newtup if no toasting is needed, or a palloc'd modified tuple
 *    that is what should actually get stored
 *
 * NOTE: neither newtup nor oldtup will be modified.  This is a change
 * from the pre-8.1 API of this routine.
 * ----------
 */
HeapTuple
toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
                       int options)
{// #lizard forgives
    HeapTuple    result_tuple;
    TupleDesc    tupleDesc;
    Form_pg_attribute *att;
    int            numAttrs;
    int            i;

    bool        need_change = false;
    bool        need_free = false;
    bool        need_delold = false;
    bool        has_nulls = false;

    Size        maxDataLen;
    Size        hoff;

    char        toast_action[MaxHeapAttributeNumber];
    bool        toast_isnull[MaxHeapAttributeNumber];
    bool        toast_oldisnull[MaxHeapAttributeNumber];
    Datum        toast_values[MaxHeapAttributeNumber];
    Datum        toast_oldvalues[MaxHeapAttributeNumber];
    struct varlena *toast_oldexternal[MaxHeapAttributeNumber];
    int32        toast_sizes[MaxHeapAttributeNumber];
    bool        toast_free[MaxHeapAttributeNumber];
    bool        toast_delold[MaxHeapAttributeNumber];

    /*
     * Ignore the INSERT_SPECULATIVE option. Speculative insertions/super
     * deletions just normally insert/delete the toast values. It seems
     * easiest to deal with that here, instead on, potentially, multiple
     * callers.
     */
    options &= ~HEAP_INSERT_SPECULATIVE;

    /*
     * We should only ever be called for tuples of plain relations or
     * materialized views --- recursing on a toast rel is bad news.
     */
    Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
           rel->rd_rel->relkind == RELKIND_MATVIEW);

    /*
     * Get the tuple descriptor and break down the tuple(s) into fields.
     */
    tupleDesc = rel->rd_att;
    att = tupleDesc->attrs;
    numAttrs = tupleDesc->natts;

    Assert(numAttrs <= MaxHeapAttributeNumber);
    heap_deform_tuple(newtup, tupleDesc, toast_values, toast_isnull);
    if (oldtup != NULL)
        heap_deform_tuple(oldtup, tupleDesc, toast_oldvalues, toast_oldisnull);

    /* ----------
     * Then collect information about the values given
     *
     * NOTE: toast_action[i] can have these values:
     *        ' '        default handling
     *        'p'        already processed --- don't touch it
     *        'x'        incompressible, but OK to move off
     *
     * NOTE: toast_sizes[i] is only made valid for varlena attributes with
     *        toast_action[i] different from 'p'.
     * ----------
     */
    memset(toast_action, ' ', numAttrs * sizeof(char));
    memset(toast_oldexternal, 0, numAttrs * sizeof(struct varlena *));
    memset(toast_free, 0, numAttrs * sizeof(bool));
    memset(toast_delold, 0, numAttrs * sizeof(bool));

    for (i = 0; i < numAttrs; i++)
    {
        struct varlena *old_value;
        struct varlena *new_value;

        if (oldtup != NULL)
        {
            /*
             * For UPDATE get the old and new values of this attribute
             */
            old_value = (struct varlena *) DatumGetPointer(toast_oldvalues[i]);
            new_value = (struct varlena *) DatumGetPointer(toast_values[i]);

            /*
             * If the old value is stored on disk, check if it has changed so
             * we have to delete it later.
             */
            if (att[i]->attlen == -1 && !toast_oldisnull[i] &&
                VARATT_IS_EXTERNAL_ONDISK(old_value))
            {
                if (toast_isnull[i] || !VARATT_IS_EXTERNAL_ONDISK(new_value) ||
                    memcmp((char *) old_value, (char *) new_value,
                           VARSIZE_EXTERNAL(old_value)) != 0)
                {
                    /*
                     * The old external stored value isn't needed any more
                     * after the update
                     */
                    toast_delold[i] = true;
                    need_delold = true;
                }
                else
                {
                    /*
                     * This attribute isn't changed by this update so we reuse
                     * the original reference to the old value in the new
                     * tuple.
                     */
                    toast_action[i] = 'p';
                    continue;
                }
            }
        }
        else
        {
            /*
             * For INSERT simply get the new value
             */
            new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
        }

        /*
         * Handle NULL attributes
         */
        if (toast_isnull[i])
        {
            toast_action[i] = 'p';
            has_nulls = true;
            continue;
        }

        /*
         * Now look at varlena attributes
         */
        if (att[i]->attlen == -1)
        {
            /*
             * If the table's attribute says PLAIN always, force it so.
             */
            if (att[i]->attstorage == 'p')
                toast_action[i] = 'p';

            /*
             * We took care of UPDATE above, so any external value we find
             * still in the tuple must be someone else's that we cannot reuse
             * (this includes the case of an out-of-line in-memory datum).
             * Fetch it back (without decompression, unless we are forcing
             * PLAIN storage).  If necessary, we'll push it out as a new
             * external value below.
             */
            if (VARATT_IS_EXTERNAL(new_value))
            {
                toast_oldexternal[i] = new_value;
                if (att[i]->attstorage == 'p')
                    new_value = heap_tuple_untoast_attr(new_value);
                else
                    new_value = heap_tuple_fetch_attr(new_value);
                toast_values[i] = PointerGetDatum(new_value);
                toast_free[i] = true;
                need_change = true;
                need_free = true;
            }

            /*
             * Remember the size of this attribute
             */
            toast_sizes[i] = VARSIZE_ANY(new_value);
        }
        else
        {
            /*
             * Not a varlena attribute, plain storage always
             */
            toast_action[i] = 'p';
        }
    }

    /* ----------
     * Compress and/or save external until data fits into target length
     *
     *    1: Inline compress attributes with attstorage 'x', and store very
     *       large attributes with attstorage 'x' or 'e' external immediately
     *    2: Store attributes with attstorage 'x' or 'e' external
     *    3: Inline compress attributes with attstorage 'm'
     *    4: Store attributes with attstorage 'm' external
     * ----------
     */

    /* compute header overhead --- this should match heap_form_tuple() */
    hoff = SizeofHeapTupleHeader;
    if (has_nulls)
        hoff += BITMAPLEN(numAttrs);
    if (newtup->t_data->t_infomask & HEAP_HASOID)
        hoff += sizeof(Oid);
    hoff = MAXALIGN(hoff);
    /* now convert to a limit on the tuple data size */
    maxDataLen = TOAST_TUPLE_TARGET - hoff;

    /*
     * Look for attributes with attstorage 'x' to compress.  Also find large
     * attributes with attstorage 'x' or 'e', and store them external.
     */
    while (heap_compute_data_size(tupleDesc,
                                  toast_values, toast_isnull) > maxDataLen)
    {
        int            biggest_attno = -1;
        int32        biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
        Datum        old_value;
        Datum        new_value;

        /*
         * Search for the biggest yet unprocessed internal attribute
         */
        for (i = 0; i < numAttrs; i++)
        {
            if (toast_action[i] != ' ')
                continue;
            if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
                continue;        /* can't happen, toast_action would be 'p' */
            if (VARATT_IS_COMPRESSED(DatumGetPointer(toast_values[i])))
                continue;
            if (att[i]->attstorage != 'x' && att[i]->attstorage != 'e')
                continue;
            if (toast_sizes[i] > biggest_size)
            {
                biggest_attno = i;
                biggest_size = toast_sizes[i];
            }
        }

        if (biggest_attno < 0)
            break;

        /*
         * Attempt to compress it inline, if it has attstorage 'x'
         */
        i = biggest_attno;
        if (att[i]->attstorage == 'x')
        {
            old_value = toast_values[i];
            new_value = toast_compress_datum(old_value);

            if (DatumGetPointer(new_value) != NULL)
            {
                /* successful compression */
                if (toast_free[i])
                    pfree(DatumGetPointer(old_value));
                toast_values[i] = new_value;
                toast_free[i] = true;
                toast_sizes[i] = VARSIZE(DatumGetPointer(toast_values[i]));
                need_change = true;
                need_free = true;
            }
            else
            {
                /* incompressible, ignore on subsequent compression passes */
                toast_action[i] = 'x';
            }
        }
        else
        {
            /* has attstorage 'e', ignore on subsequent compression passes */
            toast_action[i] = 'x';
        }

        /*
         * If this value is by itself more than maxDataLen (after compression
         * if any), push it out to the toast table immediately, if possible.
         * This avoids uselessly compressing other fields in the common case
         * where we have one long field and several short ones.
         *
         * XXX maybe the threshold should be less than maxDataLen?
         */
        if (toast_sizes[i] > maxDataLen &&
            rel->rd_rel->reltoastrelid != InvalidOid)
        {
            old_value = toast_values[i];
            toast_action[i] = 'p';
            toast_values[i] = toast_save_datum(rel, toast_values[i],
                                               toast_oldexternal[i], options
#ifdef _SHARDING_
                                               ,HeapTupleGetShardId(newtup)
#endif
                                                );
            if (toast_free[i])
                pfree(DatumGetPointer(old_value));
            toast_free[i] = true;
            need_change = true;
            need_free = true;
        }
    }

    /*
     * Second we look for attributes of attstorage 'x' or 'e' that are still
     * inline.  But skip this if there's no toast table to push them to.
     */
    while (heap_compute_data_size(tupleDesc,
                                  toast_values, toast_isnull) > maxDataLen &&
           rel->rd_rel->reltoastrelid != InvalidOid)
    {
        int            biggest_attno = -1;
        int32        biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
        Datum        old_value;

        /*------
         * Search for the biggest yet inlined attribute with
         * attstorage equals 'x' or 'e'
         *------
         */
        for (i = 0; i < numAttrs; i++)
        {
            if (toast_action[i] == 'p')
                continue;
            if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
                continue;        /* can't happen, toast_action would be 'p' */
            if (att[i]->attstorage != 'x' && att[i]->attstorage != 'e')
                continue;
            if (toast_sizes[i] > biggest_size)
            {
                biggest_attno = i;
                biggest_size = toast_sizes[i];
            }
        }

        if (biggest_attno < 0)
            break;

        /*
         * Store this external
         */
        i = biggest_attno;
        old_value = toast_values[i];
        toast_action[i] = 'p';
        toast_values[i] = toast_save_datum(rel, toast_values[i],
                                           toast_oldexternal[i], options
#ifdef _SHARDING_
                                            ,HeapTupleGetShardId(newtup)
#endif
                                            );
        if (toast_free[i])
            pfree(DatumGetPointer(old_value));
        toast_free[i] = true;

        need_change = true;
        need_free = true;
    }

    /*
     * Round 3 - this time we take attributes with storage 'm' into
     * compression
     */
    while (heap_compute_data_size(tupleDesc,
                                  toast_values, toast_isnull) > maxDataLen)
    {
        int            biggest_attno = -1;
        int32        biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
        Datum        old_value;
        Datum        new_value;

        /*
         * Search for the biggest yet uncompressed internal attribute
         */
        for (i = 0; i < numAttrs; i++)
        {
            if (toast_action[i] != ' ')
                continue;
            if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
                continue;        /* can't happen, toast_action would be 'p' */
            if (VARATT_IS_COMPRESSED(DatumGetPointer(toast_values[i])))
                continue;
            if (att[i]->attstorage != 'm')
                continue;
            if (toast_sizes[i] > biggest_size)
            {
                biggest_attno = i;
                biggest_size = toast_sizes[i];
            }
        }

        if (biggest_attno < 0)
            break;

        /*
         * Attempt to compress it inline
         */
        i = biggest_attno;
        old_value = toast_values[i];
        new_value = toast_compress_datum(old_value);

        if (DatumGetPointer(new_value) != NULL)
        {
            /* successful compression */
            if (toast_free[i])
                pfree(DatumGetPointer(old_value));
            toast_values[i] = new_value;
            toast_free[i] = true;
            toast_sizes[i] = VARSIZE(DatumGetPointer(toast_values[i]));
            need_change = true;
            need_free = true;
        }
        else
        {
            /* incompressible, ignore on subsequent compression passes */
            toast_action[i] = 'x';
        }
    }

    /*
     * Finally we store attributes of type 'm' externally.  At this point we
     * increase the target tuple size, so that 'm' attributes aren't stored
     * externally unless really necessary.
     */
    maxDataLen = TOAST_TUPLE_TARGET_MAIN - hoff;

    while (heap_compute_data_size(tupleDesc,
                                  toast_values, toast_isnull) > maxDataLen &&
           rel->rd_rel->reltoastrelid != InvalidOid)
    {
        int            biggest_attno = -1;
        int32        biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
        Datum        old_value;

        /*--------
         * Search for the biggest yet inlined attribute with
         * attstorage = 'm'
         *--------
         */
        for (i = 0; i < numAttrs; i++)
        {
            if (toast_action[i] == 'p')
                continue;
            if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
                continue;        /* can't happen, toast_action would be 'p' */
            if (att[i]->attstorage != 'm')
                continue;
            if (toast_sizes[i] > biggest_size)
            {
                biggest_attno = i;
                biggest_size = toast_sizes[i];
            }
        }

        if (biggest_attno < 0)
            break;

        /*
         * Store this external
         */
        i = biggest_attno;
        old_value = toast_values[i];
        toast_action[i] = 'p';
        toast_values[i] = toast_save_datum(rel, toast_values[i],
                                           toast_oldexternal[i], options
#ifdef _SHARDING_
                                            ,HeapTupleGetShardId(newtup)
#endif
                                            );
        if (toast_free[i])
            pfree(DatumGetPointer(old_value));
        toast_free[i] = true;

        need_change = true;
        need_free = true;
    }

    /*
     * In the case we toasted any values, we need to build a new heap tuple
     * with the changed values.
     */
    if (need_change)
    {
        HeapTupleHeader olddata = newtup->t_data;
        HeapTupleHeader new_data;
        int32        new_header_len;
        int32        new_data_len;
        int32        new_tuple_len;

        /*
         * Calculate the new size of the tuple.
         *
         * Note: we used to assume here that the old tuple's t_hoff must equal
         * the new_header_len value, but that was incorrect.  The old tuple
         * might have a smaller-than-current natts, if there's been an ALTER
         * TABLE ADD COLUMN since it was stored; and that would lead to a
         * different conclusion about the size of the null bitmap, or even
         * whether there needs to be one at all.
         */
        new_header_len = SizeofHeapTupleHeader;
        if (has_nulls)
            new_header_len += BITMAPLEN(numAttrs);
        if (olddata->t_infomask & HEAP_HASOID)
            new_header_len += sizeof(Oid);
        new_header_len = MAXALIGN(new_header_len);
        new_data_len = heap_compute_data_size(tupleDesc,
                                              toast_values, toast_isnull);
        new_tuple_len = new_header_len + new_data_len;

        /*
         * Allocate and zero the space needed, and fill HeapTupleData fields.
         */
        result_tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + new_tuple_len);
        result_tuple->t_len = new_tuple_len;
        result_tuple->t_self = newtup->t_self;
        result_tuple->t_tableOid = newtup->t_tableOid;
#ifdef PGXC
        result_tuple->t_xc_node_id = newtup->t_xc_node_id;
#endif

        new_data = (HeapTupleHeader) ((char *) result_tuple + HEAPTUPLESIZE);
        result_tuple->t_data = new_data;

        /*
         * Copy the existing tuple header, but adjust natts and t_hoff.
         */
        memcpy(new_data, olddata, SizeofHeapTupleHeader);
        HeapTupleHeaderSetNatts(new_data, numAttrs);
        new_data->t_hoff = new_header_len;
        if (olddata->t_infomask & HEAP_HASOID)
            HeapTupleHeaderSetOid(new_data, HeapTupleHeaderGetOid(olddata));

        /* Copy over the data, and fill the null bitmap if needed */
        heap_fill_tuple(tupleDesc,
                        toast_values,
                        toast_isnull,
                        (char *) new_data + new_header_len,
                        new_data_len,
                        &(new_data->t_infomask),
                        has_nulls ? new_data->t_bits : NULL);
    }
    else
        result_tuple = newtup;

    /*
     * Free allocated temp values
     */
    if (need_free)
        for (i = 0; i < numAttrs; i++)
            if (toast_free[i])
                pfree(DatumGetPointer(toast_values[i]));

    /*
     * Delete external values from the old tuple
     */
    if (need_delold)
        for (i = 0; i < numAttrs; i++)
            if (toast_delold[i])
                toast_delete_datum(rel, toast_oldvalues[i], false);

    return result_tuple;
}


/* ----------
 * toast_flatten_tuple -
 *
 *    "Flatten" a tuple to contain no out-of-line toasted fields.
 *    (This does not eliminate compressed or short-header datums.)
 *
 *    Note: we expect the caller already checked HeapTupleHasExternal(tup),
 *    so there is no need for a short-circuit path.
 * ----------
 */
HeapTuple
toast_flatten_tuple(HeapTuple tup, TupleDesc tupleDesc)
{
    HeapTuple    new_tuple;
    Form_pg_attribute *att = tupleDesc->attrs;
    int            numAttrs = tupleDesc->natts;
    int            i;
    Datum        toast_values[MaxTupleAttributeNumber];
    bool        toast_isnull[MaxTupleAttributeNumber];
    bool        toast_free[MaxTupleAttributeNumber];

    /*
     * Break down the tuple into fields.
     */
    Assert(numAttrs <= MaxTupleAttributeNumber);
    heap_deform_tuple(tup, tupleDesc, toast_values, toast_isnull);

    memset(toast_free, 0, numAttrs * sizeof(bool));

    for (i = 0; i < numAttrs; i++)
    {
        /*
         * Look at non-null varlena attributes
         */
        if (!toast_isnull[i] && att[i]->attlen == -1)
        {
            struct varlena *new_value;

            new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
            if (VARATT_IS_EXTERNAL(new_value))
            {
                new_value = heap_tuple_fetch_attr(new_value);
                toast_values[i] = PointerGetDatum(new_value);
                toast_free[i] = true;
            }
        }
    }

    /*
     * Form the reconfigured tuple.
     */
    new_tuple = heap_form_tuple(tupleDesc, toast_values, toast_isnull);

    /*
     * Be sure to copy the tuple's OID and identity fields.  We also make a
     * point of copying visibility info, just in case anybody looks at those
     * fields in a syscache entry.
     */
    if (tupleDesc->tdhasoid)
        HeapTupleSetOid(new_tuple, HeapTupleGetOid(tup));

    new_tuple->t_self = tup->t_self;
    new_tuple->t_tableOid = tup->t_tableOid;

    new_tuple->t_data->t_choice = tup->t_data->t_choice;
    new_tuple->t_data->t_ctid = tup->t_data->t_ctid;
    new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK;
    new_tuple->t_data->t_infomask |=
        tup->t_data->t_infomask & HEAP_XACT_MASK;
    new_tuple->t_data->t_infomask2 &= ~HEAP2_XACT_MASK;
    new_tuple->t_data->t_infomask2 |=
        tup->t_data->t_infomask2 & HEAP2_XACT_MASK;

    /*
     * Free allocated temp values
     */
    for (i = 0; i < numAttrs; i++)
        if (toast_free[i])
            pfree(DatumGetPointer(toast_values[i]));

    return new_tuple;
}


/* ----------
 * toast_flatten_tuple_to_datum -
 *
 *    "Flatten" a tuple containing out-of-line toasted fields into a Datum.
 *    The result is always palloc'd in the current memory context.
 *
 *    We have a general rule that Datums of container types (rows, arrays,
 *    ranges, etc) must not contain any external TOAST pointers.  Without
 *    this rule, we'd have to look inside each Datum when preparing a tuple
 *    for storage, which would be expensive and would fail to extend cleanly
 *    to new sorts of container types.
 *
 *    However, we don't want to say that tuples represented as HeapTuples
 *    can't contain toasted fields, so instead this routine should be called
 *    when such a HeapTuple is being converted into a Datum.
 *
 *    While we're at it, we decompress any compressed fields too.  This is not
 *    necessary for correctness, but reflects an expectation that compression
 *    will be more effective if applied to the whole tuple not individual
 *    fields.  We are not so concerned about that that we want to deconstruct
 *    and reconstruct tuples just to get rid of compressed fields, however.
 *    So callers typically won't call this unless they see that the tuple has
 *    at least one external field.
 *
 *    On the other hand, in-line short-header varlena fields are left alone.
 *    If we "untoasted" them here, they'd just get changed back to short-header
 *    format anyway within heap_fill_tuple.
 * ----------
 */
Datum
toast_flatten_tuple_to_datum(HeapTupleHeader tup,
                             uint32 tup_len,
                             TupleDesc tupleDesc)
{// #lizard forgives
    HeapTupleHeader new_data;
    int32        new_header_len;
    int32        new_data_len;
    int32        new_tuple_len;
    HeapTupleData tmptup;
    Form_pg_attribute *att = tupleDesc->attrs;
    int            numAttrs = tupleDesc->natts;
    int            i;
    bool        has_nulls = false;
    Datum        toast_values[MaxTupleAttributeNumber];
    bool        toast_isnull[MaxTupleAttributeNumber];
    bool        toast_free[MaxTupleAttributeNumber];

    /* Build a temporary HeapTuple control structure */
    tmptup.t_len = tup_len;
    ItemPointerSetInvalid(&(tmptup.t_self));
    tmptup.t_tableOid = InvalidOid;
#ifdef PGXC
    tmptup.t_xc_node_id = 0;
#endif
    tmptup.t_data = tup;

    /*
     * Break down the tuple into fields.
     */
    Assert(numAttrs <= MaxTupleAttributeNumber);
    heap_deform_tuple(&tmptup, tupleDesc, toast_values, toast_isnull);

    memset(toast_free, 0, numAttrs * sizeof(bool));

    for (i = 0; i < numAttrs; i++)
    {
        /*
         * Look at non-null varlena attributes
         */
        if (toast_isnull[i])
            has_nulls = true;
        else if (att[i]->attlen == -1)
        {
            struct varlena *new_value;

            new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
            if (VARATT_IS_EXTERNAL(new_value) ||
                VARATT_IS_COMPRESSED(new_value))
            {
                new_value = heap_tuple_untoast_attr(new_value);
                toast_values[i] = PointerGetDatum(new_value);
                toast_free[i] = true;
            }
        }
    }

    /*
     * Calculate the new size of the tuple.
     *
     * This should match the reconstruction code in toast_insert_or_update.
     */
    new_header_len = SizeofHeapTupleHeader;
    if (has_nulls)
        new_header_len += BITMAPLEN(numAttrs);
    if (tup->t_infomask & HEAP_HASOID)
        new_header_len += sizeof(Oid);
    new_header_len = MAXALIGN(new_header_len);
    new_data_len = heap_compute_data_size(tupleDesc,
                                          toast_values, toast_isnull);
    new_tuple_len = new_header_len + new_data_len;

    new_data = (HeapTupleHeader) palloc0(new_tuple_len);

    /*
     * Copy the existing tuple header, but adjust natts and t_hoff.
     */
    memcpy(new_data, tup, SizeofHeapTupleHeader);
    HeapTupleHeaderSetNatts(new_data, numAttrs);
    new_data->t_hoff = new_header_len;
    if (tup->t_infomask & HEAP_HASOID)
        HeapTupleHeaderSetOid(new_data, HeapTupleHeaderGetOid(tup));

    /* Set the composite-Datum header fields correctly */
    HeapTupleHeaderSetDatumLength(new_data, new_tuple_len);
    HeapTupleHeaderSetTypeId(new_data, tupleDesc->tdtypeid);
    HeapTupleHeaderSetTypMod(new_data, tupleDesc->tdtypmod);

    /* Copy over the data, and fill the null bitmap if needed */
    heap_fill_tuple(tupleDesc,
                    toast_values,
                    toast_isnull,
                    (char *) new_data + new_header_len,
                    new_data_len,
                    &(new_data->t_infomask),
                    has_nulls ? new_data->t_bits : NULL);

    /*
     * Free allocated temp values
     */
    for (i = 0; i < numAttrs; i++)
        if (toast_free[i])
            pfree(DatumGetPointer(toast_values[i]));

    return PointerGetDatum(new_data);
}


/* ----------
 * toast_build_flattened_tuple -
 *
 *    Build a tuple containing no out-of-line toasted fields.
 *    (This does not eliminate compressed or short-header datums.)
 *
 *    This is essentially just like heap_form_tuple, except that it will
 *    expand any external-data pointers beforehand.
 *
 *    It's not very clear whether it would be preferable to decompress
 *    in-line compressed datums while at it.  For now, we don't.
 * ----------
 */
HeapTuple
toast_build_flattened_tuple(TupleDesc tupleDesc,
                            Datum *values,
                            bool *isnull)
{
    HeapTuple    new_tuple;
    Form_pg_attribute *att = tupleDesc->attrs;
    int            numAttrs = tupleDesc->natts;
    int            num_to_free;
    int            i;
    Datum        new_values[MaxTupleAttributeNumber];
    Pointer        freeable_values[MaxTupleAttributeNumber];

    /*
     * We can pass the caller's isnull array directly to heap_form_tuple, but
     * we potentially need to modify the values array.
     */
    Assert(numAttrs <= MaxTupleAttributeNumber);
    memcpy(new_values, values, numAttrs * sizeof(Datum));

    num_to_free = 0;
    for (i = 0; i < numAttrs; i++)
    {
        /*
         * Look at non-null varlena attributes
         */
        if (!isnull[i] && att[i]->attlen == -1)
        {
            struct varlena *new_value;

            new_value = (struct varlena *) DatumGetPointer(new_values[i]);
            if (VARATT_IS_EXTERNAL(new_value))
            {
                new_value = heap_tuple_fetch_attr(new_value);
                new_values[i] = PointerGetDatum(new_value);
                freeable_values[num_to_free++] = (Pointer) new_value;
            }
        }
    }

    /*
     * Form the reconfigured tuple.
     */
    new_tuple = heap_form_tuple(tupleDesc, new_values, isnull);

    /*
     * Free allocated temp values
     */
    for (i = 0; i < num_to_free; i++)
        pfree(freeable_values[i]);

    return new_tuple;
}


/* ----------
 * toast_compress_datum -
 *
 *    Create a compressed version of a varlena datum
 *
 *    If we fail (ie, compressed result is actually bigger than original)
 *    then return NULL.  We must not use compressed data if it'd expand
 *    the tuple!
 *
 *    We use VAR{SIZE,DATA}_ANY so we can handle short varlenas here without
 *    copying them.  But we can't handle external or compressed datums.
 * ----------
 */
Datum
toast_compress_datum(Datum value)
{
    struct varlena *tmp;
    int32        valsize = VARSIZE_ANY_EXHDR(DatumGetPointer(value));
    int32        len;

    Assert(!VARATT_IS_EXTERNAL(DatumGetPointer(value)));
    Assert(!VARATT_IS_COMPRESSED(DatumGetPointer(value)));

    /*
     * No point in wasting a palloc cycle if value size is out of the allowed
     * range for compression
     */
    if (valsize < PGLZ_strategy_default->min_input_size ||
        valsize > PGLZ_strategy_default->max_input_size)
        return PointerGetDatum(NULL);

    tmp = (struct varlena *) palloc(PGLZ_MAX_OUTPUT(valsize) +
                                    TOAST_COMPRESS_HDRSZ);

    /*
     * We recheck the actual size even if pglz_compress() reports success,
     * because it might be satisfied with having saved as little as one byte
     * in the compressed data --- which could turn into a net loss once you
     * consider header and alignment padding.  Worst case, the compressed
     * format might require three padding bytes (plus header, which is
     * included in VARSIZE(tmp)), whereas the uncompressed format would take
     * only one header byte and no padding if the value is short enough.  So
     * we insist on a savings of more than 2 bytes to ensure we have a gain.
     */
    len = pglz_compress(VARDATA_ANY(DatumGetPointer(value)),
                        valsize,
                        TOAST_COMPRESS_RAWDATA(tmp),
                        PGLZ_strategy_default);
    if (len >= 0 &&
        len + TOAST_COMPRESS_HDRSZ < valsize - 2)
    {
        TOAST_COMPRESS_SET_RAWSIZE(tmp, valsize);
        SET_VARSIZE_COMPRESSED(tmp, len + TOAST_COMPRESS_HDRSZ);
        /* successful compression */
        return PointerGetDatum(tmp);
    }
    else
    {
        /* incompressible data */
        pfree(tmp);
        return PointerGetDatum(NULL);
    }
}


/* ----------
 * toast_get_valid_index
 *
 *    Get OID of valid index associated to given toast relation. A toast
 *    relation can have only one valid index at the same time.
 */
Oid
toast_get_valid_index(Oid toastoid, LOCKMODE lock)
{
    int            num_indexes;
    int            validIndex;
    Oid            validIndexOid;
    Relation   *toastidxs;
    Relation    toastrel;

    /* Open the toast relation */
    toastrel = heap_open(toastoid, lock);

    /* Look for the valid index of the toast relation */
    validIndex = toast_open_indexes(toastrel,
                                    lock,
                                    &toastidxs,
                                    &num_indexes);
    validIndexOid = RelationGetRelid(toastidxs[validIndex]);

    /* Close the toast relation and all its indexes */
    toast_close_indexes(toastidxs, num_indexes, lock);
    heap_close(toastrel, lock);

    return validIndexOid;
}


/* ----------
 * toast_save_datum -
 *
 *    Save one single datum into the secondary relation and return
 *    a Datum reference for it.
 *
 * rel: the main relation we're working with (not the toast rel!)
 * value: datum to be pushed to toast storage
 * oldexternal: if not NULL, toast pointer previously representing the datum
 * options: options to be passed to heap_insert() for toast rows
 * ----------
 */
static Datum
toast_save_datum(Relation rel, Datum value,
                 struct varlena *oldexternal, int options
#ifdef _SHARDING_
                , ShardID sid
#endif
                )
{// #lizard forgives
    Relation    toastrel;
    Relation   *toastidxs;
    HeapTuple    toasttup;
    TupleDesc    toasttupDesc;
    Datum        t_values[3];
    bool        t_isnull[3];
    CommandId    mycid = GetCurrentCommandId(true);
    struct varlena *result;
    struct varatt_external toast_pointer;
    union
    {
        struct varlena hdr;
        /* this is to make the union big enough for a chunk: */
        char        data[TOAST_MAX_CHUNK_SIZE + VARHDRSZ];
        /* ensure union is aligned well enough: */
        int32        align_it;
    }            chunk_data;
    int32        chunk_size;
    int32        chunk_seq = 0;
    char       *data_p;
    int32        data_todo;
    Pointer        dval = DatumGetPointer(value);
    int            num_indexes;
    int            validIndex;

    Assert(!VARATT_IS_EXTERNAL(value));

    /*
     * Open the toast relation and its indexes.  We can use the index to check
     * uniqueness of the OID we assign to the toasted item, even though it has
     * additional columns besides OID.
     */
    toastrel = heap_open(rel->rd_rel->reltoastrelid, RowExclusiveLock);
    toasttupDesc = toastrel->rd_att;

    /* Open all the toast indexes and look for the valid one */
    validIndex = toast_open_indexes(toastrel,
                                    RowExclusiveLock,
                                    &toastidxs,
                                    &num_indexes);

    /*
     * Get the data pointer and length, and compute va_rawsize and va_extsize.
     *
     * va_rawsize is the size of the equivalent fully uncompressed datum, so
     * we have to adjust for short headers.
     *
     * va_extsize is the actual size of the data payload in the toast records.
     */
    if (VARATT_IS_SHORT(dval))
    {
        data_p = VARDATA_SHORT(dval);
        data_todo = VARSIZE_SHORT(dval) - VARHDRSZ_SHORT;
        toast_pointer.va_rawsize = data_todo + VARHDRSZ;    /* as if not short */
        toast_pointer.va_extsize = data_todo;
    }
    else if (VARATT_IS_COMPRESSED(dval))
    {
        data_p = VARDATA(dval);
        data_todo = VARSIZE(dval) - VARHDRSZ;
        /* rawsize in a compressed datum is just the size of the payload */
        toast_pointer.va_rawsize = VARRAWSIZE_4B_C(dval) + VARHDRSZ;
        toast_pointer.va_extsize = data_todo;
        /* Assert that the numbers look like it's compressed */
        Assert(VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer));
    }
    else
    {
        data_p = VARDATA(dval);
        data_todo = VARSIZE(dval) - VARHDRSZ;
        toast_pointer.va_rawsize = VARSIZE(dval);
        toast_pointer.va_extsize = data_todo;
    }

    /*
     * Insert the correct table OID into the result TOAST pointer.
     *
     * Normally this is the actual OID of the target toast table, but during
     * table-rewriting operations such as CLUSTER, we have to insert the OID
     * of the table's real permanent toast table instead.  rd_toastoid is set
     * if we have to substitute such an OID.
     */
    if (OidIsValid(rel->rd_toastoid))
        toast_pointer.va_toastrelid = rel->rd_toastoid;
    else
        toast_pointer.va_toastrelid = RelationGetRelid(toastrel);

    /*
     * Choose an OID to use as the value ID for this toast value.
     *
     * Normally we just choose an unused OID within the toast table.  But
     * during table-rewriting operations where we are preserving an existing
     * toast table OID, we want to preserve toast value OIDs too.  So, if
     * rd_toastoid is set and we had a prior external value from that same
     * toast table, re-use its value ID.  If we didn't have a prior external
     * value (which is a corner case, but possible if the table's attstorage
     * options have been changed), we have to pick a value ID that doesn't
     * conflict with either new or existing toast value OIDs.
     */
    if (!OidIsValid(rel->rd_toastoid))
    {
        /* normal case: just choose an unused OID */
        toast_pointer.va_valueid =
            GetNewOidWithIndex(toastrel,
                               RelationGetRelid(toastidxs[validIndex]),
                               (AttrNumber) 1);
    }
    else
    {
        /* rewrite case: check to see if value was in old toast table */
        toast_pointer.va_valueid = InvalidOid;
        if (oldexternal != NULL)
        {
            struct varatt_external old_toast_pointer;

            Assert(VARATT_IS_EXTERNAL_ONDISK(oldexternal));
            /* Must copy to access aligned fields */
            VARATT_EXTERNAL_GET_POINTER(old_toast_pointer, oldexternal);
            if (old_toast_pointer.va_toastrelid == rel->rd_toastoid)
            {
                /* This value came from the old toast table; reuse its OID */
                toast_pointer.va_valueid = old_toast_pointer.va_valueid;

                /*
                 * There is a corner case here: the table rewrite might have
                 * to copy both live and recently-dead versions of a row, and
                 * those versions could easily reference the same toast value.
                 * When we copy the second or later version of such a row,
                 * reusing the OID will mean we select an OID that's already
                 * in the new toast table.  Check for that, and if so, just
                 * fall through without writing the data again.
                 *
                 * While annoying and ugly-looking, this is a good thing
                 * because it ensures that we wind up with only one copy of
                 * the toast value when there is only one copy in the old
                 * toast table.  Before we detected this case, we'd have made
                 * multiple copies, wasting space; and what's worse, the
                 * copies belonging to already-deleted heap tuples would not
                 * be reclaimed by VACUUM.
                 */
                if (toastrel_valueid_exists(toastrel,
                                            toast_pointer.va_valueid))
                {
                    /* Match, so short-circuit the data storage loop below */
                    data_todo = 0;
                }
            }
        }
        if (toast_pointer.va_valueid == InvalidOid)
        {
            /*
             * new value; must choose an OID that doesn't conflict in either
             * old or new toast table
             */
            do
            {
                toast_pointer.va_valueid =
                    GetNewOidWithIndex(toastrel,
                                       RelationGetRelid(toastidxs[validIndex]),
                                       (AttrNumber) 1);
            } while (toastid_valueid_exists(rel->rd_toastoid,
                                            toast_pointer.va_valueid));
        }
    }

    /*
     * Initialize constant parts of the tuple data
     */
    t_values[0] = ObjectIdGetDatum(toast_pointer.va_valueid);
    t_values[2] = PointerGetDatum(&chunk_data);
    t_isnull[0] = false;
    t_isnull[1] = false;
    t_isnull[2] = false;

    /*
     * Split up the item into chunks
     */
    while (data_todo > 0)
    {
        int            i;

        CHECK_FOR_INTERRUPTS();

        /*
         * Calculate the size of this chunk
         */
        chunk_size = Min(TOAST_MAX_CHUNK_SIZE, data_todo);

        /*
         * Build a tuple and store it
         */
        t_values[1] = Int32GetDatum(chunk_seq++);
        SET_VARSIZE(&chunk_data, chunk_size + VARHDRSZ);
        memcpy(VARDATA(&chunk_data), data_p, chunk_size);
        toasttup = heap_form_tuple_toast(toasttupDesc, t_values, t_isnull, sid);

        heap_insert(toastrel, toasttup, mycid, options, NULL);

        /*
         * Create the index entry.  We cheat a little here by not using
         * FormIndexDatum: this relies on the knowledge that the index columns
         * are the same as the initial columns of the table for all the
         * indexes.  We also cheat by not providing an IndexInfo: this is okay
         * for now because btree doesn't need one, but we might have to be
         * more honest someday.
         *
         * Note also that there had better not be any user-created index on
         * the TOAST table, since we don't bother to update anything else.
         */
        for (i = 0; i < num_indexes; i++)
        {
            /* Only index relations marked as ready can be updated */
            if (IndexIsReady(toastidxs[i]->rd_index))
                index_insert(toastidxs[i], t_values, t_isnull,
                             &(toasttup->t_self),
                             toastrel,
                             toastidxs[i]->rd_index->indisunique ?
                             UNIQUE_CHECK_YES : UNIQUE_CHECK_NO,
                             NULL);
        }

        /*
         * Free memory
         */
        heap_freetuple(toasttup);

        /*
         * Move on to next chunk
         */
        data_todo -= chunk_size;
        data_p += chunk_size;
    }

    /*
     * Done - close toast relation and its indexes
     */
    toast_close_indexes(toastidxs, num_indexes, RowExclusiveLock);
    heap_close(toastrel, RowExclusiveLock);

    /*
     * Create the TOAST pointer value that we'll return
     */
    result = (struct varlena *) palloc(TOAST_POINTER_SIZE);
    SET_VARTAG_EXTERNAL(result, VARTAG_ONDISK);
    memcpy(VARDATA_EXTERNAL(result), &toast_pointer, sizeof(toast_pointer));

    return PointerGetDatum(result);
}


/* ----------
 * toast_delete_datum -
 *
 *    Delete a single external stored value.
 * ----------
 */
static void
toast_delete_datum(Relation rel, Datum value, bool is_speculative)
{
    struct varlena *attr = (struct varlena *) DatumGetPointer(value);
    struct varatt_external toast_pointer;
    Relation    toastrel;
    Relation   *toastidxs;
    ScanKeyData toastkey;
    SysScanDesc toastscan;
    HeapTuple    toasttup;
    int            num_indexes;
    int            validIndex;
    SnapshotData SnapshotToast;

    if (!VARATT_IS_EXTERNAL_ONDISK(attr))
        return;

    /* Must copy to access aligned fields */
    VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);

    /*
     * Open the toast relation and its indexes
     */
    toastrel = heap_open(toast_pointer.va_toastrelid, RowExclusiveLock);

    /* Fetch valid relation used for process */
    validIndex = toast_open_indexes(toastrel,
                                    RowExclusiveLock,
                                    &toastidxs,
                                    &num_indexes);

    /*
     * Setup a scan key to find chunks with matching va_valueid
     */
    ScanKeyInit(&toastkey,
                (AttrNumber) 1,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(toast_pointer.va_valueid));

    /*
     * Find all the chunks.  (We don't actually care whether we see them in
     * sequence or not, but since we've already locked the index we might as
     * well use systable_beginscan_ordered.)
     */
    init_toast_snapshot(&SnapshotToast);
    toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
                                           &SnapshotToast, 1, &toastkey);
    while ((toasttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
    {
        /*
         * Have a chunk, delete it
         */
        if (is_speculative)
            heap_abort_speculative(toastrel, toasttup);
        else
            simple_heap_delete(toastrel, &toasttup->t_self);
    }

    /*
     * End scan and close relations
     */
    systable_endscan_ordered(toastscan);
    toast_close_indexes(toastidxs, num_indexes, RowExclusiveLock);
    heap_close(toastrel, RowExclusiveLock);
}


/* ----------
 * toastrel_valueid_exists -
 *
 * Test whether a toast value with the given ID exists in the toast relation.
 * For safety, we consider a value to exist if there are either live or dead
 * toast rows with that ID; see notes for GetNewOid().
 * ----------
 */
static bool
toastrel_valueid_exists(Relation toastrel, Oid valueid)
{
    bool        result = false;
    ScanKeyData toastkey;
    SysScanDesc toastscan;
    int            num_indexes;
    int            validIndex;
    Relation   *toastidxs;

    /* Fetch a valid index relation */
    validIndex = toast_open_indexes(toastrel,
                                    RowExclusiveLock,
                                    &toastidxs,
                                    &num_indexes);

    /*
     * Setup a scan key to find chunks with matching va_valueid
     */
    ScanKeyInit(&toastkey,
                (AttrNumber) 1,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(valueid));

    /*
     * Is there any such chunk?
     */
    toastscan = systable_beginscan(toastrel,
                                   RelationGetRelid(toastidxs[validIndex]),
								   true, SnapshotAny, 1, &toastkey);

    if (systable_getnext(toastscan) != NULL)
        result = true;

    systable_endscan(toastscan);

    /* Clean up */
    toast_close_indexes(toastidxs, num_indexes, RowExclusiveLock);

    return result;
}

/* ----------
 * toastid_valueid_exists -
 *
 *    As above, but work from toast rel's OID not an open relation
 * ----------
 */
static bool
toastid_valueid_exists(Oid toastrelid, Oid valueid)
{
    bool        result;
    Relation    toastrel;

    toastrel = heap_open(toastrelid, AccessShareLock);

    result = toastrel_valueid_exists(toastrel, valueid);

    heap_close(toastrel, AccessShareLock);

    return result;
}


/* ----------
 * toast_fetch_datum -
 *
 *    Reconstruct an in memory Datum from the chunks saved
 *    in the toast relation
 * ----------
 */
static struct varlena *
toast_fetch_datum(struct varlena *attr)
{// #lizard forgives
    Relation    toastrel;
    Relation   *toastidxs;
    ScanKeyData toastkey;
    SysScanDesc toastscan;
    HeapTuple    ttup;
    TupleDesc    toasttupDesc;
    struct varlena *result;
    struct varatt_external toast_pointer;
    int32        ressize;
    int32        residx,
                nextidx;
    int32        numchunks;
    Pointer        chunk;
    bool        isnull;
    char       *chunkdata;
    int32        chunksize;
    int            num_indexes;
    int            validIndex;
    SnapshotData SnapshotToast;

    if (!VARATT_IS_EXTERNAL_ONDISK(attr))
        elog(ERROR, "toast_fetch_datum shouldn't be called for non-ondisk datums");

    /* Must copy to access aligned fields */
    VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);

    ressize = toast_pointer.va_extsize;
    numchunks = ((ressize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;

    result = (struct varlena *) palloc(ressize + VARHDRSZ);

    if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
        SET_VARSIZE_COMPRESSED(result, ressize + VARHDRSZ);
    else
        SET_VARSIZE(result, ressize + VARHDRSZ);

    /*
     * Open the toast relation and its indexes
     */
    toastrel = heap_open(toast_pointer.va_toastrelid, AccessShareLock);
    toasttupDesc = toastrel->rd_att;

    /* Look for the valid index of the toast relation */
    validIndex = toast_open_indexes(toastrel,
                                    AccessShareLock,
                                    &toastidxs,
                                    &num_indexes);

    /*
     * Setup a scan key to fetch from the index by va_valueid
     */
    ScanKeyInit(&toastkey,
                (AttrNumber) 1,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(toast_pointer.va_valueid));

    /*
     * Read the chunks by index
     *
     * Note that because the index is actually on (valueid, chunkidx) we will
     * see the chunks in chunkidx order, even though we didn't explicitly ask
     * for it.
     */
    nextidx = 0;

    init_toast_snapshot(&SnapshotToast);
    toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
                                           &SnapshotToast, 1, &toastkey);
    while ((ttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
    {
        /*
         * Have a chunk, extract the sequence number and the data
         */
        residx = DatumGetInt32(fastgetattr(ttup, 2, toasttupDesc, &isnull));
        Assert(!isnull);
        chunk = DatumGetPointer(fastgetattr(ttup, 3, toasttupDesc, &isnull));
        Assert(!isnull);
        if (!VARATT_IS_EXTENDED(chunk))
        {
            chunksize = VARSIZE(chunk) - VARHDRSZ;
            chunkdata = VARDATA(chunk);
        }
        else if (VARATT_IS_SHORT(chunk))
        {
            /* could happen due to heap_form_tuple doing its thing */
            chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
            chunkdata = VARDATA_SHORT(chunk);
        }
        else
        {
            /* should never happen */
            elog(ERROR, "found toasted toast chunk for toast value %u in %s",
                 toast_pointer.va_valueid,
                 RelationGetRelationName(toastrel));
            chunksize = 0;        /* keep compiler quiet */
            chunkdata = NULL;
        }

        /*
         * Some checks on the data we've found
         */
        if (residx != nextidx)
            elog(ERROR, "unexpected chunk number %d (expected %d) for toast value %u in %s",
                 residx, nextidx,
                 toast_pointer.va_valueid,
                 RelationGetRelationName(toastrel));
        if (residx < numchunks - 1)
        {
            if (chunksize != TOAST_MAX_CHUNK_SIZE)
                elog(ERROR, "unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s",
                     chunksize, (int) TOAST_MAX_CHUNK_SIZE,
                     residx, numchunks,
                     toast_pointer.va_valueid,
                     RelationGetRelationName(toastrel));
        }
        else if (residx == numchunks - 1)
        {
            if ((residx * TOAST_MAX_CHUNK_SIZE + chunksize) != ressize)
                elog(ERROR, "unexpected chunk size %d (expected %d) in final chunk %d for toast value %u in %s",
                     chunksize,
                     (int) (ressize - residx * TOAST_MAX_CHUNK_SIZE),
                     residx,
                     toast_pointer.va_valueid,
                     RelationGetRelationName(toastrel));
        }
        else
            elog(ERROR, "unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
                 residx,
                 0, numchunks - 1,
                 toast_pointer.va_valueid,
                 RelationGetRelationName(toastrel));

        /*
         * Copy the data into proper place in our result
         */
        memcpy(VARDATA(result) + residx * TOAST_MAX_CHUNK_SIZE,
               chunkdata,
               chunksize);

        nextidx++;
    }

    /*
     * Final checks that we successfully fetched the datum
     */
    if (nextidx != numchunks)
        elog(ERROR, "missing chunk number %d for toast value %u in %s",
             nextidx,
             toast_pointer.va_valueid,
             RelationGetRelationName(toastrel));

    /*
     * End scan and close relations
     */
    systable_endscan_ordered(toastscan);
    toast_close_indexes(toastidxs, num_indexes, AccessShareLock);
    heap_close(toastrel, AccessShareLock);

    return result;
}

/* ----------
 * toast_fetch_datum_slice -
 *
 *    Reconstruct a segment of a Datum from the chunks saved
 *    in the toast relation
 * ----------
 */
static struct varlena *
toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset, int32 length)
{// #lizard forgives
    Relation    toastrel;
    Relation   *toastidxs;
    ScanKeyData toastkey[3];
    int            nscankeys;
    SysScanDesc toastscan;
    HeapTuple    ttup;
    TupleDesc    toasttupDesc;
    struct varlena *result;
    struct varatt_external toast_pointer;
    int32        attrsize;
    int32        residx;
    int32        nextidx;
    int            numchunks;
    int            startchunk;
    int            endchunk;
    int32        startoffset;
    int32        endoffset;
    int            totalchunks;
    Pointer        chunk;
    bool        isnull;
    char       *chunkdata;
    int32        chunksize;
    int32        chcpystrt;
    int32        chcpyend;
    int            num_indexes;
    int            validIndex;
    SnapshotData SnapshotToast;

    if (!VARATT_IS_EXTERNAL_ONDISK(attr))
        elog(ERROR, "toast_fetch_datum_slice shouldn't be called for non-ondisk datums");

    /* Must copy to access aligned fields */
    VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);

    /*
     * It's nonsense to fetch slices of a compressed datum -- this isn't lo_*
     * we can't return a compressed datum which is meaningful to toast later
     */
    Assert(!VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer));

    attrsize = toast_pointer.va_extsize;
    totalchunks = ((attrsize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;

    if (sliceoffset >= attrsize)
    {
        sliceoffset = 0;
        length = 0;
    }

    if (((sliceoffset + length) > attrsize) || length < 0)
        length = attrsize - sliceoffset;

    result = (struct varlena *) palloc(length + VARHDRSZ);

    if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
        SET_VARSIZE_COMPRESSED(result, length + VARHDRSZ);
    else
        SET_VARSIZE(result, length + VARHDRSZ);

    if (length == 0)
        return result;            /* Can save a lot of work at this point! */

    startchunk = sliceoffset / TOAST_MAX_CHUNK_SIZE;
    endchunk = (sliceoffset + length - 1) / TOAST_MAX_CHUNK_SIZE;
    numchunks = (endchunk - startchunk) + 1;

    startoffset = sliceoffset % TOAST_MAX_CHUNK_SIZE;
    endoffset = (sliceoffset + length - 1) % TOAST_MAX_CHUNK_SIZE;

    /*
     * Open the toast relation and its indexes
     */
    toastrel = heap_open(toast_pointer.va_toastrelid, AccessShareLock);
    toasttupDesc = toastrel->rd_att;

    /* Look for the valid index of toast relation */
    validIndex = toast_open_indexes(toastrel,
                                    AccessShareLock,
                                    &toastidxs,
                                    &num_indexes);

    /*
     * Setup a scan key to fetch from the index. This is either two keys or
     * three depending on the number of chunks.
     */
    ScanKeyInit(&toastkey[0],
                (AttrNumber) 1,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(toast_pointer.va_valueid));

    /*
     * Use equality condition for one chunk, a range condition otherwise:
     */
    if (numchunks == 1)
    {
        ScanKeyInit(&toastkey[1],
                    (AttrNumber) 2,
                    BTEqualStrategyNumber, F_INT4EQ,
                    Int32GetDatum(startchunk));
        nscankeys = 2;
    }
    else
    {
        ScanKeyInit(&toastkey[1],
                    (AttrNumber) 2,
                    BTGreaterEqualStrategyNumber, F_INT4GE,
                    Int32GetDatum(startchunk));
        ScanKeyInit(&toastkey[2],
                    (AttrNumber) 2,
                    BTLessEqualStrategyNumber, F_INT4LE,
                    Int32GetDatum(endchunk));
        nscankeys = 3;
    }

    /*
     * Read the chunks by index
     *
     * The index is on (valueid, chunkidx) so they will come in order
     */
    init_toast_snapshot(&SnapshotToast);
    nextidx = startchunk;
    toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
                                           &SnapshotToast, nscankeys, toastkey);
    while ((ttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
    {
        /*
         * Have a chunk, extract the sequence number and the data
         */
        residx = DatumGetInt32(fastgetattr(ttup, 2, toasttupDesc, &isnull));
        Assert(!isnull);
        chunk = DatumGetPointer(fastgetattr(ttup, 3, toasttupDesc, &isnull));
        Assert(!isnull);
        if (!VARATT_IS_EXTENDED(chunk))
        {
            chunksize = VARSIZE(chunk) - VARHDRSZ;
            chunkdata = VARDATA(chunk);
        }
        else if (VARATT_IS_SHORT(chunk))
        {
            /* could happen due to heap_form_tuple doing its thing */
            chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
            chunkdata = VARDATA_SHORT(chunk);
        }
        else
        {
            /* should never happen */
            elog(ERROR, "found toasted toast chunk for toast value %u in %s",
                 toast_pointer.va_valueid,
                 RelationGetRelationName(toastrel));
            chunksize = 0;        /* keep compiler quiet */
            chunkdata = NULL;
        }

        /*
         * Some checks on the data we've found
         */
        if ((residx != nextidx) || (residx > endchunk) || (residx < startchunk))
            elog(ERROR, "unexpected chunk number %d (expected %d) for toast value %u in %s",
                 residx, nextidx,
                 toast_pointer.va_valueid,
                 RelationGetRelationName(toastrel));
        if (residx < totalchunks - 1)
        {
            if (chunksize != TOAST_MAX_CHUNK_SIZE)
                elog(ERROR, "unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s when fetching slice",
                     chunksize, (int) TOAST_MAX_CHUNK_SIZE,
                     residx, totalchunks,
                     toast_pointer.va_valueid,
                     RelationGetRelationName(toastrel));
        }
        else if (residx == totalchunks - 1)
        {
            if ((residx * TOAST_MAX_CHUNK_SIZE + chunksize) != attrsize)
                elog(ERROR, "unexpected chunk size %d (expected %d) in final chunk %d for toast value %u in %s when fetching slice",
                     chunksize,
                     (int) (attrsize - residx * TOAST_MAX_CHUNK_SIZE),
                     residx,
                     toast_pointer.va_valueid,
                     RelationGetRelationName(toastrel));
        }
        else
            elog(ERROR, "unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
                 residx,
                 0, totalchunks - 1,
                 toast_pointer.va_valueid,
                 RelationGetRelationName(toastrel));

        /*
         * Copy the data into proper place in our result
         */
        chcpystrt = 0;
        chcpyend = chunksize - 1;
        if (residx == startchunk)
            chcpystrt = startoffset;
        if (residx == endchunk)
            chcpyend = endoffset;

        memcpy(VARDATA(result) +
               (residx * TOAST_MAX_CHUNK_SIZE - sliceoffset) + chcpystrt,
               chunkdata + chcpystrt,
               (chcpyend - chcpystrt) + 1);

        nextidx++;
    }

    /*
     * Final checks that we successfully fetched the datum
     */
    if (nextidx != (endchunk + 1))
        elog(ERROR, "missing chunk number %d for toast value %u in %s",
             nextidx,
             toast_pointer.va_valueid,
             RelationGetRelationName(toastrel));

    /*
     * End scan and close relations
     */
    systable_endscan_ordered(toastscan);
    toast_close_indexes(toastidxs, num_indexes, AccessShareLock);
    heap_close(toastrel, AccessShareLock);

    return result;
}

/* ----------
 * toast_decompress_datum -
 *
 * Decompress a compressed version of a varlena datum
 */
static struct varlena *
toast_decompress_datum(struct varlena *attr)
{
    struct varlena *result;

    Assert(VARATT_IS_COMPRESSED(attr));

    result = (struct varlena *)
        palloc(TOAST_COMPRESS_RAWSIZE(attr) + VARHDRSZ);
    SET_VARSIZE(result, TOAST_COMPRESS_RAWSIZE(attr) + VARHDRSZ);

    if (pglz_decompress(TOAST_COMPRESS_RAWDATA(attr),
                        VARSIZE(attr) - TOAST_COMPRESS_HDRSZ,
                        VARDATA(result),
                        TOAST_COMPRESS_RAWSIZE(attr)) < 0)
        elog(ERROR, "compressed data is corrupted");

    return result;
}


/* ----------
 * toast_open_indexes
 *
 *    Get an array of the indexes associated to the given toast relation
 *    and return as well the position of the valid index used by the toast
 *    relation in this array. It is the responsibility of the caller of this
 *    function to close the indexes as well as free them.
 */
static int
toast_open_indexes(Relation toastrel,
                   LOCKMODE lock,
                   Relation **toastidxs,
                   int *num_indexes)
{
    int            i = 0;
    int            res = 0;
    bool        found = false;
    List       *indexlist;
    ListCell   *lc;

    /* Get index list of the toast relation */
    indexlist = RelationGetIndexList(toastrel);
    Assert(indexlist != NIL);

    *num_indexes = list_length(indexlist);

    /* Open all the index relations */
    *toastidxs = (Relation *) palloc(*num_indexes * sizeof(Relation));
    foreach(lc, indexlist)
        (*toastidxs)[i++] = index_open(lfirst_oid(lc), lock);

    /* Fetch the first valid index in list */
    for (i = 0; i < *num_indexes; i++)
    {
        Relation    toastidx = (*toastidxs)[i];

        if (toastidx->rd_index->indisvalid)
        {
            res = i;
            found = true;
            break;
        }
    }

    /*
     * Free index list, not necessary anymore as relations are opened and a
     * valid index has been found.
     */
    list_free(indexlist);

    /*
     * The toast relation should have one valid index, so something is going
     * wrong if there is nothing.
     */
    if (!found)
        elog(ERROR, "no valid index found for toast relation with Oid %u",
             RelationGetRelid(toastrel));

    return res;
}

/* ----------
 * toast_close_indexes
 *
 *    Close an array of indexes for a toast relation and free it. This should
 *    be called for a set of indexes opened previously with toast_open_indexes.
 */
static void
toast_close_indexes(Relation *toastidxs, int num_indexes, LOCKMODE lock)
{
    int            i;

    /* Close relations and clean up things */
    for (i = 0; i < num_indexes; i++)
        index_close(toastidxs[i], lock);
    pfree(toastidxs);
}

/* ----------
 * init_toast_snapshot
 *
 *    Initialize an appropriate TOAST snapshot.  We must use an MVCC snapshot
 *    to initialize the TOAST snapshot; since we don't know which one to use,
 *    just use the oldest one.  This is safe: at worst, we will get a "snapshot
 *    too old" error that might have been avoided otherwise.
 */
static void
init_toast_snapshot(Snapshot toast_snapshot)
{
    Snapshot    snapshot = GetOldestSnapshot();

    if (snapshot == NULL)
        elog(ERROR, "no known snapshots");

    InitToastSnapshot(*toast_snapshot, snapshot->lsn, snapshot->whenTaken);
}
